Thermal ripple-compensating, gain-flattening filter for an optical amplifier

Abstract

An optical device including an optical amplifier to amplify optical signals received through an optical input, and to supply the amplified optical signals from an optical output, and an optical filter component to compensate for variations in the gain spectrum of the optical amplifier that occur as a function of wavelength and operating temperature. The optical filter component includes a first optical filter having an athermalized transmission spectrum and a second optical filter having a transmission (or insertion loss) spectrum that varies as a function of operating temperature.

The invention claimed is:  
     
       1. An optical device having an optical input and output, said optical device comprising: 
       an optical amplifier to amplify optical signals received through the optical input of the device; and  
       an optical filter component to compensate for variations in the gain spectrum of said optical amplifier that occur as a function of wavelength and operating temperature, wherein said optical filter component includes a first optical filter having an athermalized transmission spectrum, and a second optical filter having a transmission spectrum that varies as a function of operating temperature.  
     
     
       2. The optical device of  claim 1 , wherein said optical amplifier includes an erbium-doped fiber. 
     
     
       3. The optical device of  claim 1 , wherein said optical amplifier is a discrete Raman amplifier. 
     
     
       4. The optical device of  claim 1 , wherein said optical amplifier includes a doped waveguide. 
     
     
       5. The optical device of  claim 1 , wherein said first optical filter comprises a multi-layer stack of alternating layers of a first material having a high index of refraction and a second material having a low index of refraction. 
     
     
       6. The optical device of  claim 1 , wherein said first optical filter comprises a fiber Bragg grating. 
     
     
       7. The optical device of  claim 1 , wherein said second optical filter comprises a fiber Bragg grating. 
     
     
       8. The optical device of  claim 1 , wherein said second optical filter has an insertion loss whose first order derivative with respect to operating temperature is substantially equal to the linearized first order derivative of the gain of the optical amplifier with respect to the operating temperature, wherein the first order derivatives are not equal to zero. 
     
     
       9. The optical device of  claim 4 , wherein said second optical filter comprises a fiber Bragg grating. 
     
     
       10. An optical filter for flattening the gain of an optical amplifier that has a gain spectrum that varies as a function of operating temperature, said optical filter comprising: 
       a first optical filter portion having an athermalized transmission spectrum; and  
       a second optical filter portion having a transmission spectrum that varies as a function of operating temperature,  
       wherein said first and second optical filter portions compensate for variations in the gain spectrum of said optical amplifier that occur as a function of wavelength and operating temperature.  
     
     
       11. The optical filter of  claim 10 , wherein said first optical filter portion comprises a multi-layer stack of alternating layers of a first material having a high index of refraction and a second material having a low index of refraction. 
     
     
       12. The optical filter of  claim 10 , wherein said second optical filter portion comprises a fiber Bragg grating. 
     
     
       13. The optical filter of  claim 11 , wherein said second optical filter portion comprises a fiber Bragg grating. 
     
     
       14. A method of compensating for variations in the gain spectrum of an optical amplifier that occur with fluctuations in operating temperature, the method comprising the steps of: 
       providing a first optical filter having an athermalized insertion loss spectrum; and  
       providing a second optical filter having an insertion loss spectrum that varies with fluctuations in operating temperature, and that, when combined with the insertion loss spectrum of the first optical filter, compensates for variations in the optical amplifier gain as a function of wavelength.